This invention relates to highly durable alumina-spinel monolithic refractories.
Alumina monolithic refractories have been commonly used for lining ladles, vacuum-degassing vessels, hot-metal mixers, blast-furnace troughs and their covers, hot-metal mixer cars, tundishes and the like. However, they are damaged as a result of erosion caused by FeO,MnO or CaO contained in the molten metal or slag or as a result of structual spalling induced by the penetration of slag. To prevent the penetration of the slag, all attempts have been made to add carbon, silicon carbide and other elements that are less likely to be wet by slag. However, it has been found that such added elements do not function properly when they become oxidized. When added in large quantities, furthermore, they have proved to cause structural deterioration and heavier erosion upon oxidation.
Alumina-spinel monolithic refractories combined with MgO-Al.sub.2 O.sub.3 spinel clinker (hereinafter called spinel clinker) have also been proposed. Japanese Provisional Patent Publication No. 55-23004, for example, discloses a material consisting of 10-85 percent by weight of spinel clinker, 5-30 percent by weight of alumina, and 10-25 percent by weight of high-alumina cement. Japanese Provisional Patent Publication No. 59-128271 discloses a material consisting of 50-95 percent by weight of spinel and a remainder of aluminum oxide. Japanese Provisional Patent Publication No. 60 -60985 discloses a material consisting of at least 60 parts by weight of spinel clinker, 10-35 parts by weight of alumina clinker and 10-10 parts by weight of alumina cement. Spinel clinkers are free of the problems associated with oxidation. When combined with alumina clinker, they become less likely to produce low melting point substances.
Conventional alumina spinel monolithic refractories have been useful as refractories for various applications, notably for ladles and vacuum degassing vessels. Recently, however, furnaces have come to be operated under increasingly severe conditions. Also, there is a pressing need to decrease the consumption of refractories. Therefor, more durable monolithic refractories are in great demand.